Tag Archives: Harmane

Laminin-integrin interactions can in some settings activate the extracellular signal-regulated

Laminin-integrin interactions can in some settings activate the extracellular signal-regulated kinases (ERKs) but the control mechanisms are poorly understood. ERK activation. Moreover the Harmane responding cell line expressed the two integrin α6 splice variants α6A and α6B whereas the nonresponding cell line expressed only α6B. Furthermore ERK activation was seen in cells transfected with the integrin α6A subunit but not in α6B-transfected cells. We conclude that laminin-1 and -10/11 share the ability to induce ERK activation that this is regulated by integrin α6Aβ1 and suggest a novel role for dystroglycan-binding laminin domains as suppressors of this activation. INTRODUCTION Laminins are basement membrane components composed of heterotrimers of α β and γ chains (Colognato and Yurchenco 2000 ). Both laminin-1 (α1β1γ1) and laminin-10/11 (α5β1γ1/α5β2γ1) Harmane seem to have important functions in embryogenesis. Laminin-1 is thought to be important for early epithelial morphogenesis in many tissues (Klein (1996 ). However this integrin may activate ERK in some settings (Gonzales (1999 ). It is possible that Harmane only some ligands for α3β1 integrin can activate ERK or that the α3A and α3B cytoplasmic splice variants differ in their signaling capacity. These possibilities should be analyzed further with cells of defined expression of such variants (DiPersio (2001 ) hypothesized that the presence of coreceptors might be necessary for integrin α6β1-mediated ERK activation. Herein we demonstrate suppression of this activation by a coreceptor. The dystroglycan antibody IIH6 suppressed integrin α6Aβ1-induced ERK activation in WI-26 VA4 cells. A similar decrease was obtained by recombinant laminin fragment α1LG4-5 which binds dystroglycan with high affinity but lacks integrin-binding sites (Talts 1999 ). Recombinant laminin fragments with capacity to bind both dystroglycan and integrin α6β1 (Talts (2000 Harmane ). However some binding to the α5-containing laminin-10/11 was noted but the binding was weak. Binding of laminin-10/11 could be abolished by EDTA suggesting divalent cation dependence. Overlay assays also demonstrated binding of laminin-10/11 to dystroglycan isolated both from muscle and a tissue rich in epithelium (kidney). Binding of laminin α1LG4 to dystroglycan can be blocked by heparin (Talts et al. 1999 ) and a heparin-sensitive cell binding site was recently mapped to mouse α5LG4 (Nielsen et al. 2000 ). Yet laminin-10/11 binding to dystroglycan in overlay assays was not perturbed by heparin suggesting that heparin and dystroglycan binding requires distinct sites. Heparin-insensitive binding to dystroglycan has been shown also for laminin-2/4 (Pall et al. 1996 ; Talts et al. 1999 ). The quantitative binding studies showing a clear hierarchy among laminin isoforms for α-dystroglycan binding are in reasonable agreement both with structural predictions (Hohenester et al. 1999 ; Timpl et al. 2000 ) and the report that α5LG1-5 can interact with dystroglycan (Shimizu et al. 1999 ). Measured binding affinities in cell free assays of some integrins to laminins are also rather low although these interactions are of obvious biological importance. For instance integrin α3β1 had a low binding activity of >600 nM for laminin-5 in conditions reflecting those found in tissues and bound laminin-10/11 even less efficiently (Eble et al. 1998 ). Recombinant α5LG4-5 was recently shown to contain the dystroglycan-binding site in another study (Yu and Talts 2003 ) and was in the present study shown to be a potent inhibitor of laminin-10/11-mediated ERK activation. This was evident in 60-min assays but not in 30-min assays carried out with laminin E8 as the substratum. The differences may be explained by the low affinity of Harmane laminin-10/11 modules to dystroglycan or other unknown differences in the binding mechanisms. The finding is notable considering the low affinity of the interaction but strongly supports the view that the dystroglycan-binding domains of laminins can suppress ERK activation. Pparg Hence the recognition of laminin-10/11 by α-dystroglycan might play a significant role in the modulation of signaling cascades initiated by laminins and integrins. Acknowledgments We thank Dr. T. Olofsson (Department of Medicine Lund University Lund Sweden) for the help with FACS analyses. This work was supported by a postdoctoral stipend from Wenner-Gren Foundation to Y.K. and a postdoctoral stipend to M.D. and.